upload-pack.c: fix filter spec quoting bug

upload-pack.c: fix filter spec quoting bug

Fix a bug in upload-pack.c that occurs when you combine partial
clone and uploadpack.packObjectsHook. You can reproduce it as
follows:

    git clone -u 'git -c uploadpack.allowfilter '\
	'-c uploadpack.packobjectshook=env '\
	'upload-pack' --filter=blob:none --no-local \
	src.git dst.git

Be careful with the line endings because this has a long quoted
string as the -u argument.

The error I get when I run this is:

	Cloning into '/tmp/broken'...
	remote: fatal: invalid filter-spec ''blob:none''
	error: git upload-pack: git-pack-objects died with error.
	fatal: git upload-pack: aborting due to possible repository corruption on the remote side.
	remote: aborting due to possible repository corruption on the remote side.
	fatal: early EOF
	fatal: index-pack failed

The problem is caused by unneeded quoting.

This bug was already present in 10ac85c785 (upload-pack: add object
filtering for partial clone, 2017-12-08) when the server side filter
support was introduced.  In fact, in 10ac85c785 this was broken
regardless of uploadpack.packObjectsHook. Then in 0b6069fe0a
(fetch-pack: test support excluding large blobs, 2017-12-08) the
quoting was removed but only behind a conditional that depends on
whether uploadpack.packObjectsHook is set.

Because uploadpack.packObjectsHook is apparently rarely used, nobody
noticed the problematic quoting could still happen.

Remove the conditional quoting and add a test for partial clone in
t5544-pack-objects-hook.

Signed-off-by: Jacob Vosmaer <jacob@gitlab.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>